Modular Optronic Periscope

ABSTRACT

A modular optronic periscope includes a staring module, having a plurality of static sensors providing image data for a wide field of view at moderate resolution, and an image processor, by way of which image data from the static sensors are stitched together into a single continuous image. A multi-spectral, narrow field of view at a higher resolution than the staring module is produced using a pointing module including a rotatable mirror, and a collimated optical bundle from the pointing module is imaged by way of an optical platform onto photosensitive devices to form a two dimensional image array. Each pixel of the image array is repositioned by way of image derotation circuitry before display.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/356,923, filed on Jun. 21, 2010, the contents of which are herebyincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present inventions relate to submarine periscopes, particularlythose that do not penetrate the submarine hull, but may also be usablewith periscopes that do penetrate the submarine hull.

2. Description of Related Art

Conventional periscopes enable a submarine to remain in contact with theabove-water environment either visually or by use of electronic sensors.Typical capabilities include imaging (visual and/or other wavelengthbands), RF/microwave communications, microwave radar, RF/microwaveintercept, GPS, etc. The periscope may penetrate the hull of thesubmarine, or it may be a non-penetrating design, in which case allsensors are electronic and signals (electrical and/or fiber optic) arerelayed to and enter the hull through a specially designed,pressure-proof, hull interface connector. Periscopes are generallydesigned such that either the entire external pressure boundary rotates(as in a conventional periscope) or some portion of the exteriorboundary rotates (optronic periscope) in order to direct the line ofsight of its optical subsystems to a desired direction.

The requirement that the pressure vessel rotate imposes severalrequirements on the design of a periscope in general and an optronicperiscope in particular. Principal among these are (a) the need to drivethe comparatively high inertia and seal friction of the rotatingsubassembly with a sufficiently large torque motor, (b) a dynamic highpressure seal that prevents water intrusion into the joint between therotating and non-rotating elements, and (c) multiple electrical andfiber optic commutation channels that permit efficient and continuouspower and signal continuity between the rotating and stationary parts ofthe system. Moreover, situational awareness may be restricted becausethe optical line of sight must be physically scanned over the horizon,generally rendering it impossible to observe the entire 360 degreepanorama at any given instant of time.

Therefore, the invention disclosed herein provides the followingadvantages and improvements over current periscope technology:

(a) The elimination of a hydraulic high pressure dynamic seal for highersystem reliability and longer life;

(b) A reduction in size, weight and power of mechanisms, hardware andassociated electronics required to direct the line of sight. Thisprovides a concurrent improvement in response time for directing theline of sight and an overall improvement in reliability;

(c) the removal of electrical commutation devices that are potentialpoints of failure and that limit the number and type of sensors that canbe deployed on a periscope; and

(d) improved situational awareness achieved through multi-spectralpanoramic imaging in which displayed images are stabilized digitallywithout moving parts for high reliability.

SUMMARY OF THE INVENTION

It is a primary objective of the invention to eliminate (a) thenecessity for large, rotational electro-mechanical subassemblies, (b)the dynamic high pressure seal, and (c) the many electrical and fiberoptic commutation channels required in the more conventional embodimentby employing a static outer structure that does not rotate and thereforerequires no commutation. A secondary objective is to employ staringcameras together with video processing technology to increasesituational awareness while permitting concurrent execution of normalsurveillance operations.

According to one embodiment of the invention, a modular optronicperiscope includes a staring module that has a plurality of staticsensors providing image data for a wide field of view at moderateresolution, and an image processor, by way of which image data from thestatic sensors are stitched together into a single continuous image. Amulti-spectral, narrow field of view at a higher resolution than thestaring module is produced using a pointing module that includes arotatable mirror. An optical bundle from the pointing module is imagedby way of an optical platform onto photosensitive devices to form a twodimensional image array. Each pixel of the image array is repositionedby way of image derotation circuitry before the display, or opticalderotation before the sensors. In a preferred embodiment, the opticalbundle from the pointing module is a collimated optical bundle. Inanother preferred arrangement, the collimated optical bundle isseparated into smaller spectral wavebands.

The periscope may include a plurality of static sensors that detectvisible light, infrared light, or both types of light, and may alsoinclude a low inertia rotatable mirror, which, preferably, is inertiallystabilized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of conventional arrangements in whicheither an entire external pressure boundary rotates (as in aconventional periscope) or some portion of the exterior boundary rotates(optronic periscope) in order to direct the line of sight of its opticalsubsystems to a desired direction.

FIG. 2 shows component parts of one embodiment of a modular optronicperiscope according to the invention.

FIG. 2A is a block diagram illustrating the arrangement of variouscomponents in the embodiment of FIG. 2.

FIG. 3 is a functional block diagram illustrating image derotationthrough high speed image processing.

FIG. 4 is a functional block diagram illustrating image derotation usingconventional optical hardware.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 2 and 2A, a Visible Staring Module 1 and a separateInfrared Staring Module 2 provide wide field of regard coverage forsituational awareness in the visible and infrared wavebands. These areshown as separate and independent structures that might also be combinedinto a single assembly. Each module is self-contained and functionsindependently of the other and also of the Pointing Module describedbelow. These staring modules are static, containing no moving parts, andeach covers 360 degrees of azimuth. As such, they require no mechanicalline of sight control, no dynamic pressure seals and no electricalcommutation. Staring modules that image in other wavebands may beadditionally incorporated into the configuration or they may replace oneor more of the modules of the embodiment described herein. These Modulesare configured with built-in interface connections that enable quick andeasy removal and installation.

Each of the Staring Modules 1 and 2 is self contained andpressure-proof, consisting of a pressure-resistant housing that containsa number of imaging sensors each having an optical aperture. Themultiple optical apertures are protected from the external environmentwith windows fabricated of a suitable optical material (such as fusedsilica, germanium, etc.) as best determined by the wavelength ofinterest. Material thickness is sufficient to withstand the requiredhydrostatic pressure. Behind each aperture is an imaging optic and anappropriate imaging sensor (e.g., visible camera, IR camera, etc.). Thenumber of sensors/apertures, their respective optical fields of view,and the pixel count of the imaging sensors are selected so as to provide360 degrees of azimuth coverage at the desired spatial resolution(instantaneous field of view) measured in pixels per degree. In oneembodiment, the sensors may provide a nominal pixel resolution ofapproximately 0.33 mRad in the visible waveband, although other spatialresolutions may be provided. Each window is sealed to the housingconventional high pressure static sealing methods such as o-rings.

Whereas each sensor in a Staring Module delivers separate image data,such data from the several sensors may be stitched together to form asingle continuous image or the data may be electronically sampled so asto display any desired portion of the complete image. Both operationsmay also be performed concurrently using an image processing techniquesuch as that disclosed in U.S. Patent Application Publication No.2009/0058988 A1 to Strzempko et al., the entire disclosure of which isincorporated herein by reference as non-essential material. Image motioncaused by movement of the submarine platform is removed using imagestabilization techniques also disclosed in the Strzempko et al.application referenced above.

Suitable hardware is required to perform the image processing functionsoutlined above. Additionally, other hardware (such as fiber opticmodulators) may also be required to, for example, transmit image data toonboard systems. As determined by the system architecture and by spaceallowances, this hardware may be located internal to the mast, inlocations such as on or near the Optical Platform (described below), orinboard of the submarine hull.

Practical constraints on the number of sensors that may be housed in aStaring Module as well as technical limits on the maximum number ofpixels available in a given sensor imposes limits on the maximumachievable spatial resolution. Available pixel densities readily allowlow to moderate spatial resolutions to be achieved in the StaringModules, enabling missions such as situational awareness, safetyassessment, and surveillance of objects at relatively close range.

Whereas the Staring Modules 1 and 2 mentioned above are typicallyconfigured for low to moderate spatial resolution for accomplishingtasks such as situational awareness and short range surveillance, theVisible/Infrared Pointing Module 3, operating in conjunction with theOptical Platform 5, constitute a narrow field of view, high resolution,multi-spectral optical system that permits surveillance (e.g.,detection/recognition) of objects at long range. In a preferredembodiment, the narrow field of view encompasses approximately fourdegrees or less of azimuth. The high resolution system formed by thePointing Module and Optical Platform functions independently of theStaring Modules. This allows long range surveillance to be conductedconcurrently with situational awareness and short range surveillance.

A stationary dome of the appropriate material and dimensions forms theoptical window and pressure barrier for the Pointing Module 3. A largeaperture pointing mirror (that may or may not be inertially stabilized)located inside the dome steers the common, multi-spectral line of sightthrough 360 degrees of azimuth and over the desired elevation range.This mirror is located at the optical center of the dome, and isactuated by azimuth and elevation drive motors (or their equivalents).Because the mirror assembly has relatively low inertia and negligiblefriction, the driving motors are comparatively small, the required drivepower is low and the dynamic response to mirror position commands can behigh. The electrical commutation channels that provide power and controlsignals to the mirror drive elements can be of low current capacity andare few in number, greatly reducing the size and complexity ofelectrical commutation hardware typically required of current optronicperiscope system implementations.

As also shown in FIGS. 2 and 2A, an optical bundle constituting a narrowfield of view exits the Visible/Infrared Pointing Module 3 and passesthrough the center of the Staring Modules 1 and 2 to the OpticalPlatform 5. As will be understood by those skilled in the art, anoptical bundle represents the sum total of all optical ray paths thatpass from one plane to another plane along the direction of a givenoptical axis. In a preferred embodiment, the optical bundle is acollimated optical bundle. As will also be understood, an optical bundleis collimated when optical rays from a point on a distant object arerendered at approximately the same angle with respect to the opticalaxis. In the Optical Platform 5 the full spectrum, preferably collimatedoptical bundle is separated into individual smaller spectral wavebands.These separate, collimated wavebands are focused onto their respectivesensor arrays using imaging optics optimized for wavelength of operationand optical quality. The sensor arrays may be chosen based on spectralresponse, pixel count and other desired operating characteristics.Separation of the wavebands can be performed using standardwavelength-sensitive beam splitters, also known as dichroic or thin filmfilters. The inventive concept disclosed herein does not require thatthe spectral bands be separated but this would be common practice. Otherembodiments might use a combination of beam splitters and reflex mirrors(mirrors that can be switched into or out of the path to redirect anoptical bundle) to separate the spectral wavebands and focus theseparated wavebands onto suitable sensor arrays.

In a preferred embodiment, three waveband channels are accommodated,although other waveband breaks are possible. The preferred wavebandchannels are a visible channel, a mid-wave infrared channel, and ashort-wave infrared channel. A narrow band laser range finding channelis introduced into the short wave infrared path to allowtransmit/receive of laser energy for range finding purposes at awavelength that can be made safe to the human eye.

The spherical form of the refractive optical dome exhibits opticalpower, which can contribute objectionable optical aberrations.Therefore, in a preferred embodiment, a Corrector lens 7 located justdownstream of the pointing mirror recollimates the incoming beam priorto its being relayed to the imaging optics in the Optical Platform 5.

The optical dome material must exhibit a suitable combination of opticaland mechanical properties depending on the system requirements. Formulti-spectral applications, it is a requirement that the material havewell-behaved optical properties across the spectral wavebands ofinterest. In addition, for deep submergence applications the materialmust also exhibit the required structural properties. SPINEL CRYSTAL, atransparent ceramic, is identified as having suitable optical andmechanical properties.

Another material that exhibits the required properties is SAPPHIRE.Other suitable materials may exist now or be available in the future.

It is often necessary and convenient to locate particular electronicsensors and/or devices at the top-most position on a periscope (that isabove the Pointing Module 3). Moreover, electrical cables that servicethese electronic sensors and/or devices may be numerous and must passthrough the Pointing Module 3. Mechanical Struts 8 that are either partof a segmented dome structure or that are located inside the dome itselfprovide the necessary support to permit mounting hardware on top of thedome. These struts also provide a conduit within which the servicecables may be housed. The Mechanical Struts 8 are sufficiently narrow soas not to significantly obstruct the optical entrance aperture of thePointing Module 3. The potentially large numbers of cables that servethe electronic sensors and/or devices do not require commutation becausethe Pointing Module 3 and the electronic sensors and/or devices locatedabove the Pointing Module 3 do not rotate.

As the Pointing Mirror 4 rotates through 360 degrees in azimuth, theimages that are presented to the focal planes of the various Cameras 6also rotate through 360 degrees. This rotation may be compensated in twopossible ways as described below.

In the first method, image derotation is accomplished in the mannerschematically represented in FIG. 3. In this embodiment, each pixel(picture element) from the Image or Camera Array 1 is dynamicallyrepositioned by an Image Processor 4 before being displayed. Thecoordinates of each pixel are dynamically computed as determined by theazimuth position of the Pointing Mirror 2, this position being sensedwith an appropriate Position Transducer 3, such as an optical encoder orsynchro device. Depending on the size of the image array and therequired speed of processing, the Image Processor 4 may be any one of anumber of high speed computational devices such as a standard processor,an FPGA (field programmable gate array), a DSP (digital signalprocessor), a GPU (graphics processing unit) or equivalent. ImageProcessor 4 may receive image data from the Image or Camera Array 1 as astream of individual pixels. In one embodiment, the Image Processor 4can dynamically reposition the image data substantially pixel-by-pixelas individual pixels are received and output the processed (e.g.,repositioned) pixels to the display device prior to receiving subsequentpixels of the pixel stream image data from the Image or Camera Array 1.As will be readily understood, this pixel-by-pixel processing minimizesthe period of latency between the capture of image data and its displayand thus maximizes real-time situational awareness. In anotherembodiment, Image Processor 4 may dynamically reposition a grouping orneighborhood of pixels of varying size that is substantially less than afull frame and output that group or neighborhood of pixels to thedisplay device prior to receiving subsequent pixels.

The second method for achieving image derotation uses conventionaloptical hardware as schematically depicted in FIG. 4. In thisembodiment, an optic, such as a Pechan Prism 1 (or equivalent) placed inthe optical path ahead of the cameras, rotates in a direction oppositeto the image rotation so as to null out the image rotation. The rotationangle of the image is measured by a Position Transducer 2 that iscoupled to the Pointing Mirror 3 as in the previous method. A DriveMotor 4 mechanically coupled to the prism outputs position commandsignals derived from the Position Transducer 2 to rotate the Prism 1 tothe required angle.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

1. A modular optronic periscope, comprising: a staring module includinga plurality of static sensors providing image data for a wide field ofview, each static sensor having nominal pixel resolution of at leastapproximately 0.33 mRad in the visible waveband; an image processoroperable to receive image data from the plurality of static sensors andto stitch together the received image data into a single continuousimage; a pointing module including a rotatable mirror providing anoptical bundle for a multi-spectral narrow field of view of less thanapproximately four degrees and at a resolution higher than the widefield of view provided by said staring module; an optical platformoperable to image the optical bundle from said pointing module ontophotosensitive devices to form a two dimensional image array; and imagederotation circuitry operable to reposition each pixel of said imagearray before display.
 2. A modular optronic periscope according to claim1, further comprising a plurality of static sensors that detect visiblelight.
 3. A modular optronic periscope according to claim 1, furthercomprising a plurality of static sensors that detect infrared light. 4.A modular optronic periscope according to claim 1, further comprising alow inertia rotatable mirror.
 5. A modular optronic periscope accordingto claim 4, wherein said low inertia rotatable mirror is inertiallystabilized.
 6. A modular optronic periscope according to claim 1,wherein said optical bundle is a collimated optical bundle.
 7. A modularoptronic periscope according to claim 6, wherein said collimated opticalbundle is separated into smaller spectral wavebands.